A refrigeration system can be used to control an environmental condition (e.g., temperature, humidity, air quality, etc.) in a conditioned space. The refrigeration system can be configured to include a refrigeration circuit (a compressor, a condenser, a throttling valve, an evaporator, etc.) and a controller. An internal combustion engine can provide power to the refrigeration system when the refrigeration system is used in a transport unit (e.g., a container on a flat car, an intermodal container, truck, a boxcar, or other similar transport unit). The internal combustion engine can include a fuel gauge to indicate how much fuel remains.